Today, a majority of the flue cured tobacco crop is cured in a curing and drying structure that is typically referred to as a bulk barn. A bulk barn includes a curing and drying chamber or section and a furnace area that includes a fan. The fan functions to circulate air into the curing and drying chamber and vertically through the tobacco afterwhich the air is either exhausted or recirculated to the furnace area where it may be heated or not heated, depending on the temperature within the barn and the particular curing and drying phase. During certain periods of the curing and drying schedule, substantial quantities of moisture must be removed from the leaf. Thus, during the process, the heated air being circulated within the curing and drying structure becomes saturated or nearly saturated with moisture and accordingly to continue to be effective in the drying process, a certain portion of this moist air must be dumped or exhausted from the curing and drying structure. There is an abundance of energy in the form of heat associated with this warm moist air that is being exhausted from a tobacco barn, especially during the leaf drying period. This means that this energy is lost. With the cost of fuel continuing to rise and the cost of bulk tobacco barns continuing to increase, it is very important and beneficial to save as much fuel as possible in curing and drying tobacco and also to be able to cure and dry a certain size crop with a minimum number of barns.
There have been attempts at incorporating heat exchangers into tobacco curing and drying structures. It has been recognized that the heat associated with the exhaust air from a curing a drying structure can be used to heat incoming fresh air. For example, there have been very simplistic approaches to this problem. Once such approach has been simply to dispose two ducts in side-by-side relationship about the end of a tobacco barn and to exhaust air through one such duct and route incoming fresh air through the other duct. In such a case, heat associated with the exhaust air to some extent at least, can be transferred to the incoming fresh air passing in the adjacent duct. Obviously, this is a very crude and inefficient system that has no flexibility whatsoever.
In addition to the simplistic, there have been very complicated approaches to providing heat exchangers for tobacco curing and drying structures. In this regard, one is referred to U.S. Pat. No. 4,499,911 which discloses a solar tobacco barn having computer operated heat exchange system for a plurality of barns. The complexities and expense of this system are obvious from a review of the '911 patent. Again, the system disclosed in this patent is quite expensive and costly to maintain, but most importantly, the system is of the type designed to accommodate a series of six barns. Therefore, the system disclosed in the Johnson U.S. Pat. No. 4,499,911, does not really address the real need of providing an effective, efficient, and reasonably priced heat exchanger for a single bulk curing barn.
Beyond that, there are literally tens of thousands of barns existing on tobacco farms today that are owned by farmers struggling to make efficient use of their energy dollar. There are no heat exchanger kits or units commercially available that enable such a heat exchange system to be retrofited to a tobacco barn.